Fix/broken sid builds

[simonbeaudoin0935]

Summary

Improve deb package build debugging and fix the fallback Qualcomm APT repository configuration
used by the reusable Debian build action.

Problem

Sid package builds were failing in GitHub Actions with missing Qualcomm build dependencies such
as qcom-libqcomtee-dev and mink-idl-compiler, while local builds were succeeding.

At the same time, build failures in CI only printed the last 500 lines of the sbuild log, which
made it harder to see the full context of the failure.

Changes

1. Update the fallback Debian repository URL in .github/actions/build_package/action.yml to use
   the canonical Artifactory APT path:

• from https://qartifactory-edge.qualcomm.com/ui/native/qsc-deb-releases
• to https://qartifactory-edge.qualcomm.com/artifactory/qsc-deb-releases

2. Print the full .build log on build failures instead of truncating output to the last 500
   lines.
3. Add AGENTS.md guidance for qcom-build-utils to document repository structure and maintenance
   expectations for future contributors.

Why this matters

• Ensures the reusable Debian package build action uses the same Qualcomm APT repository path as
  the builder images and other workflows.
• Makes CI failures much easier to diagnose by exposing the entire sbuild log in the GitHub
  Actions output.
• Captures repo-specific guidance in one place for future maintenance.

Impact

This change only affects the reusable build action and documentation in qcom-build-utils. It does
not change package contents or release behavior beyond improving dependency resolution and
failure visibility in CI.